1. Field of the Invention
The present invention relates to a starter for starting an engine.
2. Background of the Invention
As disclosed, for example, in Japanese Patent Application Laid-open No. 2005-120899, a common starter mounted on a vehicle for starting a vehicle engine includes a clutch for transmitting a drive torque generated by an electric motor to a pinion shaft movably disposed in its axial direction. The pinion shaft has a pinion gear at a front tip portion thereof, which can mesh with a ring gear of the vehicle engine. The clutch has an inner tube which is rotatably supported by a center case through a ball bearing, and to which the drive torque of the motor is transmitted.
The pinion shaft is spline-connected to an inner periphery of the inner tube at a rear side end portion thereof, and rotatably and slidably supported by a housing through a bearing at a front side end portion thereof. The pinion gear is mounted to the front tip portion of the pinion shaft, which protrudes from the bearing so as to be exposed outside the housing. In such a starter where the pinion gear is exposed outside the housing, the clutch is disposed in an enclosed space formed between the housing and the motor.
Accordingly, the conventional starter described above has a problem in that the ball bearing thereof may heat up and be damaged if an engine starting operation is repeatedly performed under extremely high temperature conditions, because the ball bearing is disposed in the enclosed space. In addition, there is a fear that water enters the starter from a fitting portion between the housing and the center case, and accumulated in the enclosed space if a temperature difference (negative pressure) between inside and outside the starter is large when the starter is flooded with water at the time of washing a car on which the starter is mounted, or when the car is running in the rain.